Investigation on the burr formation mechanism in micro cutting

It is desirable to minimize burr formation for improving part quality. This paper presents an investigation on the burr formation mechanism in micro cutting by taking into consideration the stress distribution around the cutting edge arc. The influences of the uncut chip thickness and the cutting edge radius on burr formation were investigated. Poisson burr is attributed to the side flow of the stagnation material at the bottom of the cutting edge arc. The stress distribution at the cutting edge arc has great influence on Poisson burr formation. The burr height decreases to the minimum value and then increases with reducing the uncut chip thickness due to the change of the maximum stress distribution. An optimum machining strategy also is suggested in micro milling of snake-shaped groove microstructure.     

微铣削加工刀具刃口半径影响的有限元模拟

为了分析合金钢40CrNiMoA微铣削过程中刀具刃口半径对工件受力情况的影响,采用Johnson-Cook材料模型和断裂失效模型作为工件材料模型和失效准则,采用热力耦合平面应变杂交单元并使用自适应网格技术进行网格划分,刀具与工件间的摩擦采用修正的库仑定律,进行微细铣削加工非线性弹塑性有限元模拟。通过有限元分析,得到了在相同切削速度和每齿进给量条件下,不同刃口半径下的Mises应力、最大剪应力及静水压应力的分布情况,并对结果进行了比较分析;同时讨论了实际负前角,为实际加工提供了依据。     

基于Deform 3D的刀具切削刃钝圆半径的优化设计

运用Deform 3D软件对考虑了刃口半径的切削过程进行了有限元仿真,分析了切削刃半径对加工过程对切削力和切削温度的影响。并对刀具应力及刀具磨损进行了分析,为刃口的优化设计提供了有力的依据。     

高铬铸铁的切削用量优化计算

在考虑刀具动态强度的条件下,利用有限元法对用复合陶瓷刀具加工高铬铸铁的切削用量进行了计算,为经济有效地加工高铬铸铁提供了理论依据。     

Mechanistic modeling of cutting forces in micro-end-milling considering tool run out,minimum chip thickness and tooth overlapping effects

This work proposed an improved mechanistic model for prediction of cutting forces in micro-milling process. The combined influences of tool run out, trochoidal trajectory of the tool center, overlapping of tooth, edge radius and minimum chip thickness are incorporated in this model to realize the exact cutting phenomenon. Moreover, an improved undeformed chip thickness algorithm has been presented by considering tool run out, minimum chip thickness and trajectory of all passing teeth for one complete revolution of the tool instead of only the current tooth trajectory. For estimation of tool run out, a model based on the geometry of the two fluted end mill cutter has been developed. Effects of trochoidal trajectory of the tool center and tool run out are found to be significant as each tooth has a different chip load. Further, the effect of minimum chip thickness is found to be significant at lower feed value. The proposed model has been validated by micro-milling experiments on Ti6Al4V-titanium alloys using uncoated flat end mill cutter. The predicted cutting forces were found to be in good agreement with the experimental cutting forces in both feed and cross feed directions.     

切削刀具摩擦磨损的研究方法综述

从切削试验、常规摩擦试验及特殊摩擦试验三个方面概述了国内外有关刀具材料摩擦磨损的研究方法,分析了各种方法的优缺点,最后对这一问题的重点研究方向进行了展望。     

倒圆刃刀具切削温度有限元分析

通过对不同刀尖圆弧半径的倒圆刃刀具切削加工过程进行有限元建模与分析,发现刀尖附近的温度分布将随着刀尖圆弧半径的变化而发生改变;而随着圆弧半径的增加,刀具的最高温度以及切削区域的平均温度会随之提高。     

Finite element methods for contact problems with friction

The numerical treatment of contact problems involves the formulation of the geometry, the statement of interface laws, the variational formulation and the development of algorithms. In this paper an overview with regard to the numerical simulation of frictional problems is presented when general constitutive equations are formulated in the contact interface. To be most general we will apply a geometrical model and its discretization for contact which is valid for large deformations. Furthermore the algorithms to integrate the interface laws will be discussed for the tangential stress components. Special emphasis is laid on the development of algorithms which allow an efficient treatment of frictional contact problems.     

基于刀具磨损映射关系的微细铣削力理论建模与试验研究

微细铣削加工过程中,刀具直径小且磨损较快,刀具磨损对微细铣削力有着明显的非线性影响,同时刀具跳动又对刀具每齿的磨损表现出不同的影响效应,这些影响因素会导致加工过程的不稳定性和精度.然而,目前缺乏考虑具有刀具跳动和磨损效应的通用微细铣削力模型,研究了刀具跳动与刀具每齿磨损量之间的变化规律,提出了一种同时包括刀具跳动和刀具...     

Measurement of the geometric features of a cutting tool edge with the aid of a digital image processing technique

For the further development of new machining systems such as flexible manufacturing systems (FMS), this paper reports on a new measuring system developed for the multi-purpose understanding of the geometric features of cutting tool edges having serious influences on the machining outputs. In this system, to detect three-dimensional (3D) features of the toolface and tool flank only from the two-dimensional (2D) microscopic observation of the toolface and to describe an overall 3D geometric feature of the tooledge as a digital 2D image as well as to enable inexpensive system development, two convenient measuring principles are used. These are the scanning optical section method for the toolface contour mapping and the cutting edge profile comparison method for the flank wear landwidth estimation. Based on these, experimental hardware was arranged and various processing softwares were developed. They were applied to an observation of the cutting edge wear development in some cylindrical turning experiments, to show that various effective cutting edge parameters could be easily extracted from the integrated toolface image recorded, and that sufficient accuracy and resolution for practical use could be obtained.     

A study of the effect of tool cutting edge radius on ductile cutting of silicon wafers

Ductile mode cutting of silicon wafers can be achieved under certain cutting conditions and tool geometry. An experimental investigation of the critical undeformed chip thickness in relation to the tool cutting edge radius for the brittle-ductile transition of chip formation in cutting of silicon wafers is presented in this paper. Experimental tests for cutting of silicon wafers using diamond tools of different cutting edge radii for a range of undeformed chip thickness are conducted on an ultra-precision lathe. Both ductile and brittle mode of chip formation processes are observed in the cutting tests. The results indicate that ductile cutting of silicon can be achieved at certain values of the undeformed chip thickness, which depends on the tool cutting edge radius. It is found that in cutting of silicon wafers with a certain tool cutting edge radius there is a critical value of undeformed chip thickness beyond which the chip formation changes from ductile mode to brittle mode. The ductile-brittle transition of chip formation varies with the tool cutting edge radius. Within the range of cutting conditions in the present study, it has also been found that the larger the cutting edge radius, the larger the critical undeformed chip thickness for the ductile-brittle transition in the chip formation.     

双轴切割机床龙门机架的设计与研究

设计了陶粒混凝土砌块切割机床,在切割不同规格砌块时,机床不需拆装。利用ANSYS Workbench 工具建立机床的有限元模型,通过分析得到龙门机架的最大应力、变形及其分布情况;对其进行模态分析,确定结构的振动特性,以验证龙门机架的使用性能和砌块切割的稳定性,为双轴切割机床的龙门机架设计提供进一步的理论依据。     

Investigation of the effect of cutting tool edge radius on material separation due to ductile fracture in machining

This paper investigates the interaction between cutting tool edge radius and material separation due to ductile fracture based on Atkins’ model of machining. Atkins’ machining model considers the energy needed for material separation in addition to energies required for shearing at the primary shear zone and friction at the secondary shear zone. However, the effect of cutting tool edge radius, which becomes significant at microcutting conditions, was omitted. In this study, the effect of cutting tool edge radius is included in the model and its influence on material separation is investigated. A modification to the solution methodology of Atkins’ machining model is proposed and it is shown that the shear yield stress and the fracture toughness of the work material can be calculated as a function of uncut chip thickness.     

三角形刀片切削过程的有限元分析

通过对三角形车削刀片的切削过程进行有限元分析,获得到出不同切削用量对切削力、切削温度、刀片应力的影响。可据此选择合理的切削用量以延长刀具寿命。对比有限元模拟数据与切削试验数据,发现模拟值和试验值有合理的一致性。     

Cutting surface quality analysis in micro ball end-milling of KDP crystal considering size effect and minimum undeformed chip thickness

Potassium dihydrogen phosphate (KH₂PO₄ or KDP) crystal is a typical soft-brittle optical crystal, and the size effect and brittle cutting mode are easy to appear in micro ball end-milling of KDP crystal. In this paper, micro-grooving experiments are conducted to study the size effect and brittle cutting in micro ball end-milling of KDP crystal with different feed rate and depth of cut. The cutting force, machined groove base quality and chip morphology are collected and analyzed carefully. The size effect is discovered by the phenomena of the existence of oscillations and relaxations in cutting force and hyper-proportional increase of specific cutting force, when the ratio of feed per tooth to cutting edge radius f_t/r_e is less than 1. While the brittle cutting mode is detected through the existence of sharp fluctuations in cutting force and cracks on the groove base when the ratio f_t/r_e is larger than 2. From the further comprehensive analysis of cutting force, specific cutting force, machined groove base quality and chip morphology, the cutting parameters with ratios of the maximum undeformed chip thickness in one cutting circle to cutting edge radius h_max/r_e around 0.14, 0.2 and 0.4 are regarded as size effect, optimal and brittle cutting points, respectively. The size effect, ductile cutting and brittle cutting zones are divided by the size effect and brittle cutting boundaries (points). Among the optimal points, the depth of cut of 2 μm with the ratio f_t/r_e of 1 is the optimal cutting parameter for micro ball end-milling of KDP crystal.     

切削温度对微细切削加工影响的有限元分析研究

建立微细切削仿真模型,对二维正交切削加工过程进行了热力耦合有限元数值分析,采用有限元模拟与微细切削加工实验验证相结合的方式,深入研究了切削温度对微细切削加工的影响,揭示了在高速、大切厚加工条件下,随着切削厚度的减小,刀—屑接触区切削温度降低,增加了材料的截切强度,从而引起材料的强化,导致单位切削力显著增加。     

A study of deformation of the machined workpiece and tool under different low cutting velocities with an elastic cutting tool

To understand the effects of cutting velocity, tool elastic deformation generated by high normal stresses during metal cutting processing and artificial tool flank wear on the cutting process, an iterative mathematical model for calculating the tool–workpiece contact problem was developed in this paper under the assumption of elastic cutting tools. In this model, the finite element method is used to simulate cutting of mild steel by the P20 cutting tool with constant artifical tool flank wear under the condition of three different cutting velocities. The results obtained in the simulation were found to match the experimental data reported by related studies. The simulation results also indicate that the thrust and the cutting forces are functions of cutting velocity. Besides, both the normal stress on the tool rake face and the residual stress of machined workpiece generally decrease with increase in cutting velocity. According to the findings in this study, though the residual stress of the machined workpiece decreases as the cutting velocity increases, its value is still higher than that in ordinary conditions due both to the influence of tool flank wear and tool elastic deformation. Also, the phenomenon of curvature at the workpiece end easily occurs.     

物理断裂准则应用于高速切削的研究

基于高速切削有限元模型,参照更新的拉格朗日方法在低速切削加工中的应用,将金属物理断裂准则运用于高速切削的模拟中.通过仿真分析和比较在设置物理断裂准则和几何断裂准则的两种高速切削仿真情况下,X,Y方向切削力及切屑形成的变化发现,设置了物理断裂准则的高速切削仿真得到的数据更接近实验数据,且切屑成形也与实际情况符合.     

新型微细锥形铣刀几何刃形设计与试验研究

基于切削原理及刀具结构理论,针对微细铣削加工特点,设计了新型微细锥形铣刀.通过试验研究,验证了新型微细锥形铣刀几何刃形的合理性.从而解决了锥形铣刀加工时刀具对工件挤压严重造成塑陛隆起、毛刺突出的问题.     

An edge reversal method for precision measurement of cutting edge radius of single point diamond tools

A method, which is referred to as the edge reversal method, is proposed for precision measurement of the cutting edge radius of single point diamond tools. An indentation mark of the cutting edge which replicates the cutting edge geometry is firstly made on a soft metal substrate surface. The cutting edge of the diamond tool and its indentation mark, which is regarded as the reversal cutting edge, are then measured by utilizing an atomic force microscopy (AFM), respectively. The cutting edge radius can be accurately evaluated through removing the influence of the AFM probe tip radius, which is comparable to the cutting edge radius, based on the two measured data without characterization of the AFM probe tip radius. The results of measurement experiments and uncertainty analysis are presented to demonstrate the feasibility of the proposed method.